The present invention relates generally to moisture detection systems, and more specifically to a technique and apparatus for detecting the presence of liquid phase moisture in sealed integrated circuits (IC).
It is well known that various types of device failures are attributable to the presence of moisture. Thus, for example, in sealed packages containing microelectronic devices of the integrated-circuit type, a water vapor concentration as low as several thousand parts per million can cause device failures. Accordingly, efforts have been directed at devising techniques for detecting the moisture within such a package. By detecting this moisture during the device fabrication process, it is possible initially to identify and reject failure-prone sealed packages.
The task of detecting water in sealed IC packages is alleviated by the systems disclosed in the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 3,479,862 issued to Trapp et al; PA0 U.S. Pat. No. 3,943,557 issued to Frazee et al; PA0 U.S. Pat. No. 4,050,048 issued to Frazee; PA0 U.S. Pat. No. 4,224,565 issued to Sosniak et al; and PA0 U.S. Pat. No. 4,272,986 issued to Lowry et al.
Lowry et al disclose in-situ monitoring of the moisture content of a hermetically sealed integrated circuit package by measuring the dew point of the sealed environment. The dew point is determined by lowering the temperature of the cavity at a slow, controlled rate while the surface conductivity of a conductor pattern is monitored. As the dew point temperature of the cavity environment is approached, micro-droplets of water will condense on the surface of the sensor. The sensor comprises inter-digitized aluminum conductors on a silicon oxide surface. Sosniak et al also disclose a dew point sensor for determining the moisture content of sealed integrated circuit packages.
Frazee et al are concerned with a humidity sensor for hermetically sealed semiconductor packages. The patented sensor has low resistivity and may be either a discrete humistor or may be incorporated in the semiconductor package as an integral device. A similar humidity sensor is shown in the Frazee patent. In Trapp et al the electrical resistance between two conductors on the exterior of a package is measured to determine the presence of liquid within the package.
All the other patents cited above are exemplary in the art, and are useful for moisture determination in IC packages, but all of them use a special separate sensor rather than the IC chip itself. The presence of moisture affects the electrical characteristics of integrated circuits, and a need exists to detected moisture by these changes of electrical characteristics rather than indulging in the expense of exotic humidity sensors. The present invention is intended to satisfy that need.